Apparatus for improving the flatness of rolled strips

ABSTRACT

A device for improving the flatness of metal strips during rolling, comprising a set of cylindrical rollers located side by side, located upstream of the rolling stand, independent from one another and with their respective axes parallel to the axes of the rolling cylinders, in such a manner as to correspond to the strip width. The said cylindrical rollers are so arranged as to take positions always parallel, and mutually staggered in the vertical plane by the action of servo-controls coming from detecting means for the planarity and/or the rolling tension in the strip, said last cited means being located downstream of the rolling stand, through a checking and adjusting equipment.

United States Patent 1191 [111 3,72,111; Sabatini Jan. 1, 119741 [54]APPARATUS FOR IMPROVING THE 3,499,306 3/1970 Pearson 72/17 AT S 0 ROLLEDSTRIPS 3,534,571 10/1970 Sivilotti et al.. 72/8 2,809,519 10/1957Kaestner 73/159 Inventor: Bruno Sabatml, Rome, Italy 3,581,536 6/1971Terwilliger 72/9 [73] Assignee: Centro Sperimentale Metallurgico IS.p.A., an Italian Manufacturing Primary Examiner-Milton Co" Rome [talyAtt0rneyl,rvin S. Thompson et al.

22 F1 4 1 Apr 1972 57 ABSTRACT [21 1 Appl' 240400 A device for improvingthe flatness of metal strips during rolling, comprising a set ofcylindrical rollers 10- [30] Foreign Application Priority Data catedside by side, located upstream of the rolling Apr. 22, 1971 Italy 49910A/71 Stand independent from one amther and with their respective axesparallel to the axes of the rolling cylin- 52 us. c1. 72/9, 72/17 inSuch a manner as to correspond to the Strip [511 1m. (:1 B21b 37/12Width- The Said cylindrical rollers are 80 arranged as [58] Field ofSearch 72/9. 8. 10, 12, to take Positions always Parallel, and mutuallyStag- 72/]7; 73/159 gered in the vertical plane by the action ofservocontrols coming from detecting means for the planar- 5 ReferencesCited ity and/or the rolling tension in the strip, said last citedUNITED STATES PATENTS means being located downstream of the rollingstand,

through a checking and adjusting equipment. 3,459,019 8/1969 Stone 72/122,21 1,658 8/1940 Hudson 72/234 X 1 Claim, 2 Drawing Figures 1'3 l 0 O in (1 PATENTH] JAN 1 I974 SHEET 2 0F 2 l APPARATUS FOR IMPROVING THEFLATNESS F ROLLED STRIPS The present invention relates to a device forimproving the flatness of rolled strips. More specifically, once adefect of planarity has been detected in a strip during the workingthereof, the device according to this invention allows the conditions ofrolling to be modified so as to correct said planarity defect withoutintroducing, as a consequence of the correction, any substantial changein the value of the average thickness of the rolled strip.

It is known that the defects of planarity occur during the rollingoperation of the strip when the rolling clearance between the cylindersunder load is such that the profile of the cross section of the stripissuing from the rolling mill is not geometrically similar to thecorresponding profile of the strip entering into the rolling mill, theterm rolling clearance under load meaning the gap between the rollingcylinders, in the absence of the material to be rolled, with themodifications induced by the elastic deformations undergone by thecylinders and by the other structures of the rolling mill, under theaction of the forces originated during the rolling process.

In turn the clearance between the rolling cylinders, in the absence ofthe material to be rolled, is determined by the position of the screwsfor adjustment of the stand and by the effect resulting from thecrowning or concavity obtained by the machining of the cylinders, fromthe thermal expansion of the cylinders and from their wear during therolling.

It is known that systems at present adopted for adjusting the thicknessof the strip, interfere to a greater or lesser extent, with the flatnessof the strip itself, as their action determines changes in the shape ofthe roll gap. The interference is such that for instance the correctionof a thickness error implies the introduction of a flatness defect orerror. The above interference between the thickness correction and theplanarity occurs also reversely as the correction of an error ofplanarity, with the systems used up to now, implies generally theintroduction of a change in the average thickness of the strip. Duringthe rolling operation, errors in both strip flatness and thickness mustbe corrected and conditions may arise wherein the cited interferencebetween flatness and thickness will decrease the speed of correctionand/or will cause oscillations difficult to stop.

The means at present used for rolling strip, so as to reduce flatnessand thickness errors are multiple. Even in the variety of theirembodiments, these means can be grouped under the following groups:

a. use of a sequence of rolling for the strips, having different widthsand different thicknesses, subordinated to the state of wear of thecylinders;

12. intervention from outside on the cylinders, so as to change in asuitable way the shape of the rolling clearance, by means of amodification of the crowning of the cylinders themselves. Thisintervention can be effected thermally or mechanically. If thermally, itis necessary to cool; in a suitably differentiated way, the roll tableand the expansion of the cylinders along the table will be thusadjusted. If mechanically, external forces are applied to the cylindersin order to suitably increase the elastic bending deformation, and toobtain thereon the crowning as required by the particular conditions ofrolling and to avoid thus the flatness defects.

The disadvantages deriving from the adoption of the above systems aremanifest. In case of mechanical control, the optimum rolling program forthe planarity exigencies does not coincide necessarily with the rollingprogram required by that of the orders to the rolling mill. In the caseof the thermal control of the expansion of the cylinders, the process isscarcely satisfactory as it s effect is delayed and furthermore themaximum correction which can be obtained is small due to the smallthermal gradients which can be induced between two points on the mass ofthe cylinder. Likewise, the recourse to the deformation by bending ofthe cylinders from outside is limited by the strength thereof and by thesize of the forces generally required in order to obtain adequatemodification of the roll camber. In this case it is furthermoredifficult to establish the best conditions at different points along theroll table. In fact a deformation of the cylinder which is capable ofimproving the planarity in one zone of the strip can produce a resultincompatible with the conditions of planarity induced in other zones ofthe strip.

The main purpose of the present invention is that of providing a devicewhich on the basis of the detection of the possible defects of flatnessof the strip at its outlet from the rolling stand, will allow saiddefects to be corrected without substantially interfering with theaverage thickness of the rolled strip.

Another purpose of the present invention is that of providing a processallowing the detection of the possible flatness defects during the striprolling operation and allowing also the correction of said defects by anadjustment which suitably modifies the rolling conditions of the stripswithout directly interfering with the cylinders of the stands.

The flatness defects in a strip, issuing from a rolling stand, can bedetected by devices already known in the present art, based on thedetermination of the distribution across the strip width of the rollingtension.

The object of the present invention is the provision of a device,located upstream of the stand and capable of modifying, in compliancewith the indications of one of the aforesaid detectors locateddownstream, the rolling conditions within said rolling stand, so as toimpart good flatness to the strip issuing from the stand.

The device forming the subject-matter of the present invention, isconnected, as aforesaid, to any device detecting the planarity of thestrip, located downstream of the rolling stand, and the indicativesignals of which are sent to a checking and controlling device (forinstance a computer). This equipment, from the compar' ison of saidsignals with a signal having a standard value, previously programmed,will send a correction signal which intervenes by means of the device ofthe present invention.

This device consists of a set of cylindrical rollers located side byside, mounted upstream of the rolling stand (called hereinafter the TDCset) independent from one another and normally aligned throughout thewidth of the strip. Said TDC rollers are individually independent fromone another and are capable of taking mutually staggered positions inthe vertical plane. During the rolling operation, and provided the stripentering into the stand is subjected to a pull, each roll can be made bythe aforesaid measuring and control equipment to perform a suitablevertical displacement, so that the roller itself will support theportion of strip resting on it to a greater or lesser extent, thusinducing in said portion of strip a rolling tension greater or smaller,respectively, with respect to the other portions of the strip.

Thus the rolling conditions will be modified so as to improve theflatness conditions as detected by the detection device.

The present invention will be now described with particular reference tothe attached drawings, the purpose of which is illustrative and notlimitative. Particularly in the drawings:

FIG. 1 is a diagrammatic perspective view of a rolling device accordingto this invention.

FIG. 2 is a side view of the device of FIG. 1.

As it will be noted, in said figures in order to avoid useless drawingcomplications, the parts not absolutely indispensable have been omitted.Particularly, in said figures, the reference numeral 1 denotes the stripbeing rolled, 2 is an exemplary embodiment by way of non limitativeexample, of a detection device consisting of a set of rollers (called inthe following disclosure TDM set) located downstream of the rollingstand 3; 4 is the set of rollers TDC, 5 is a transducer (one for eachTDM roller) measuring the force transmitted to each of the TDM rollersby the portion of strip bearing thereon, 6 is test and controlequipment, preferably a computer, which compares the representativesignal for the force on each TDM roller with the desired supportingforce as previously programmed and which, upon detecting the possibledeviations, will suitably modify the mutual position of the TDC rollersso as to compensate for said deviations, 7 is a transducer of thecorrecting signals sent by the computer to the rollers of the set TDC.The reference numeral 8 and 9 denote devices, for instanceelectro-hydraulic devices, rendering operative the TDM and TDC rollers.

In order to better understand the operation of the device according tothis invention, in the considered case, which however is a nonrestrictive case, let us consider the strip as subdivided into manylongitudinal portions each having a width which is a submultiple of thetotal width, and equal each to the axial length of each of the rollersof the sets TDC and TDM. Let us suppose, also that the total rollingpull will be distributed downstream of the rolling stand, so that thepull to which is subjected the portion of the strip nearest the personlooking at FIG. 2 (this zone has been dashed in FIG. 1) will be greaterthan the desired pull. At this point the anomaly will be immediatelydetected as, on the underlying roller of the TDM set, a stress will beexerted,

greater than the average stress exerted on the other rollers of the set.Through the transducer 7 and the electro-hydraulic device 9, theequipment 6 will transmit to the corresponding roller of the TDC setwhich supports the same portion of the strip, the control for itsvertical upwards movement with respect to the other rollers, so as tocontribute a greater amount of the support of the strip, with aconsequent local increase of the tension at the inlet into the rollingstand. Under these conditions the total tension will devolve to agreater extent on the portion of strip where the correction is required,and to a lesser extent on the remaining portions of the strip, andconsequently said strip portion will have a lower yield strength againstthe deformation by the cylinders and therefore a greater reduction ofthickness will be induced therein. (In fact it is known that theresistance of the material to compression by the cylinders decreaseswith the increase of the stress, to which the material is submitted, therolling deformation being a function of the pressure of the cylindersand of the tension applied to the strip). Thus the stress to which theportion of the concerned strip is subjected will tend to diminish andthus the planarity error will tend to disappear. As said mechanismoperates continuously, the rolling conditions will be the desired ones.

The present invention has been described with particular reference toits specific embodiments it, being however understood that changes orvariations might be practically adopted without departing from the scopeof the present invention as defined by the appended claims.

Having thus described the present invention, what is claimed is:

1. Apparatus for improving the flatness of metal strips during theirrolling, comprising, in combination with a rolling mill stand, aplurality of strip deflector rollers mounted upstream from the rollingmill stand for rotation about axes parallel to the axes of the rolls ofthe rolling mill stand, the total length covered by said deflectorrollers being such as to support the entire width of the rolled strip,means mounting said deflector rollers for movement transversely of theiraxes and transversely of the plane of the rolled strip independently ofeach other, and means downstream from said rolling mill stand fordetecting nonflatness of said strip across its width and forindividually moving said deflecting rollers relative to each other eachin a direction and by an amount to correct said nonflatness.

1. Apparatus for improving the flatness of metal strips during theirrolling, comprising, in combination with a rolling mill stand, aplurality of strip deflector rollers mounted upstream from the rollingmill stand for rotation about axes parallel to the axes of the rolls ofthe rolling mill stand, the total length covered by said deflectorrollers being such as to support the entire width of the rolled strip,means mounting said deflector rollers for movement transversely of theiraxes and transversely of the plane of the rolled strip independently ofeach other, and means downstream from said rolling mill stand fordetecting nonflatness of said strip across its width and forindividually moving said deflecting rollers relative to each other eachin a direction and by an amount to correct said nonflatness.